Storm overflows

Where the sewage goes

Water companies are permitted to discharge untreated sewage into rivers and the sea when it rains. Every discharge is monitored, and every monitor's readings are published. Almost nobody looks.

363,995 recorded discharges in 2025
103,442 days of discharge, added together
15,767 monitored overflows

What is happening near you?

Add your postcode and we will show the monitored overflows nearest to you, how often each one discharged, and into what.

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By company

Environment Agency Event Duration Monitoring returns for 2025. These are the audited annual figures, not the live feeds.

Company Discharges Total hours Overflows Worst single overflow
Dwr Cymru Welsh Water 96,054 779,874 2,244 Llanfachraeth WwTW — 366 times
United Utilities 57,988 312,482 2,149 Lock Lane Partington CSO — 217 times
Yorkshire Water 44,401 234,833 1,985 Marske Sewage Treatment Works — 170 times
South West Water 41,351 351,182 1,297 Shop Stw_so_shop — 243 times
Severn Trent Water 34,752 187,776 2,377 Lydney Sewage Treatment Works — 178 times
Northumbrian Water 25,771 115,524 1,499 Cotherstone STW — 161 times
Wessex Water 23,012 178,831 1,305 Hurdcott Wastewater Treatment Works — 167 times
Anglian Water 16,183 98,196 1,398 Grimsby Pyewipe Wrc and Tps — 155 times
Southern Water 14,618 109,900 917 Lavant WwTW — 166 times
Thames Water 8,922 107,230 551 Markyate Wastewater Treatment Works — 155 times
Hafren Dyfrdwy 943 6,778 45 Llanwddyn Wastewater Treatment Works — 90 times

How to read this

  • A "discharge" is one counted spill event from one overflow. Companies are permitted to do this in heavy rain — the argument is about how often, for how long, and whether the infrastructure should have been upgraded instead.
  • Where a monitor was offline for part of the year, the real figure is higher than the one shown. We flag that rather than quietly averaging it away.
  • Live status comes from each company's own near-real-time feed, which the industry states has not been through the audit process the annual returns go through. We show it, and we say so.
  • Welsh Water does not publish a live feed in the same form, so no live panel will appear in Wales even when discharges are happening.

Sources: Environment Agency EDM annual returns and the water companies' own storm overflow feeds, both published as open data.